1. Field of the Invention
This invention relates, in general, to valve assemblies, and more particularly to fast actuation, high pressure valve assemblies for use in fluid analysis systems, and methods for their use.
2. Description of Related Art
Accelerated solvent extraction is a technique for extracting solid and semisolid samples with liquid solvents. Accelerated solvent extraction uses increased temperature and pressure with common solvents to increase the efficiency of the extraction process. The accelerated solvent extraction can be used to replace more conventional Soxhlet, sonication, boiling, wrist-shaker, and other extraction methods. Several ASE systems are currently offered by the Dionex Corporation including the ASE 100, 200, and 300 Accelerated Solvent Extraction Systems.
With accelerated solvent extraction, the sample is generally first ground and/or mixed with a dispersing agent. A weighed portion is placed in a stainless steel extraction cell, which is then heated to a predetermined temperature. Initially, a conventional static valve is opened and solvent is pumped into the extraction cell and through the static valve to a collection vial. Once a desired quantity of solvent reaches the collection vial, the static valve is closed and a high pressure pump continues to fill the extraction cell with solvent until a target pressure is achieved within the extraction cell. Target pressures often are in excess of 1500 psi and in some instances target pressures of 5000 psi, or greater, are desired.
Current systems generally utilize off-the-shelf needle and seat valves that are not particularly suited for such high pressures. Also, such valves are often made from stainless steels, including 316 SST. Unfortunately, such stainless steels are not particularly compatible with some solvents and/or with some mild acids and bases. For example, 316 SST is generally not suitable for use with 1M HCl at 200° C. Nonetheless, it is increasingly desirable to utilize such solvents, acids and bases in concentrations up to 1 M and at temperatures up to 200° C. Also, such valves lack filters and often fail prematurely. When such valves fail, the entire valve generally requires replacement, often at considerable expense with significant down time.
In light of the foregoing, it would be beneficial to have a high-pressure valve assembly for fluid analysis systems which overcome the above and other disadvantages of known valve assemblies.